1. Field of the Invention
This invention relates to the field of electromagnetic interference, and in particular to a connector that suppresses electromagnetic interference from IEEE-1394 connectors.
2. Description of Related Art
The IEEE-1394 specification provides for a high speed interconnection among devices, and is particularly well suited for the high speed communication of video information among imaging devices, computers, recorders, and the like. An IEEE-1394 device operates at a bit rate of up to 400 megabits per second (higher bit rates are possible), with sharp rise and fall times. This high speed switching results in radiated emissions well into the gigahertz range. These emissions are particularly prominent at connectors, due to the relatively higher impedance introduced by the connection of pins carrying the high frequency signals.
FIG. 1 illustrates an example technique for suppressing electromagnetic interference at a connector 130 using conventional prior art techniques. Illustrated in FIG. 1 is a printed circuit board (PCB) 120 that is mounted within a chassis 110. The chassis 110 is conductive, and forms a reference ground potential 101. The connector 130 has a conductive outer shell that serves to reduce electromagnetic emissions from the pins or receptacles within the connector 130 that serve to connect external signals to components 125 on the PCB 120. The IEEE-1394 specification requires that the outer shell of the connector 130 be galvanically isolated from the reference ground potential 101. The opening 112 in the chassis 110 for the connector 130 is configured to maintain a separation between the outer shell of the connector 130 and the chassis 110. To provide the desired shielding of high-frequency electromagnetic emissions, the outer shell of the connector 130 is coupled to the chassis 110 via one or more capacitors 160. As illustrated in FIG. 1, when a cable (not shown) that is carrying the high frequency signals to the printed circuit board 120 is connected via the connector 130, a ground current path 105 is formed that travels through the outer shell of the connector 130, through a conductor 121 on the printed circuit board 120, through the capacitor 160 to a ground conductor 122 on the printed circuit board 120, and thereafter through a coupling of the conductor 122 to the chassis 110, and back along the cable.
At the very high frequencies of IEEE-1394 communications, millimeters of ground path substantially reduce the effectiveness of the connectors' electromagnetic shielding.